Punk wasn't bashing the crowd, he was being totally honest. There's a difference.
Cheap heel heat is when a guy comes out and says "This town sucks, it's sports teams suck and it's notable residents suck."
Punk's promo was more of a "I don't wrestle for the fans, I do it for myself. I didn't wrestle tonight because I love this town and wanted to entertain you. I wrestled because I wanted to, I wanted to be a star and be watched and get paid"
Now the Rock's promo on the other hand WAS generic face promo. It was all "don't insult the people, the best are the best" etc etc etc.
Every heel insults the home crowd. I agree it can be a little annoying but what do you expect. People don't always want to boo Punk especially when he's against faces people are annoyed with or don't care about and when he says things people can agree with Punk has to resort to a cheap shot at the crowd to get some heat.